The present invention relates to interface circuits for use with printers in a computer system, and is more particularly related to a single interface whose configuration may be changed dependent upon the length of the input/output cable between the printer and a host processor in the computer system.
In many computer systems, a host processor is provided having a peripheral port for providing data bits in a serial format. A peripheral adapter is provided for performing a serial-to-parallel conversion of the data bits, for buffering the data bits, and for providing handshaking between the host processor and the computer printer. In such a computer system, the peripheral adapter typically includes an interface circuit having drivers for driving data conductors in an input/output cable between the peripheral adapter and the printer, and receivers for receiving various status and handshaking data bits from the printer. Because of the resistance and distributed capacitance of the conductors in the input/output cable, the designs of the drivers and receivers in the interface circuit of the peripheral adapter, and a corresponding interface circuit is the printer, are dependent on the length of the input/output cable. Typically, if the length of the input/output cable is less than about 50 feet long, the driver and receiver in the interface circuits are single ended. If, however, the input/output cable is between about 50 feet and 492 feet long, the drivers and receiver in the interface circuits are designed using differential amplifiers.
In the past, separate interface circuits have been provided on removable boards in the peripheral adapter and printer. If the input/output cable was less than 50 feet long, a separate short line interface circuit board was installed in both the peripheral adapter and the printer. If the input/output cable was between 50 feet and 492 feet long, a separate long line interface circuit board was installed in both the peripheral adapter and the printer.